Kaolin is a fine usually white clay formed by the weathering of aluminous minerals (as feldspar) and mainly consists of kaolinite. Kaolinite is commonly represented by one or more of the chemical formulae Al4Si4O10(OH)8; Al2O3.2SiO2.2H2O; and/or Al2Si2O5(OH)4. Kaolin is one of the many industrial minerals mined today. Reserves are found in Georgia (USA), Egypt, Brazil, United Kingdom, Queensland (Australia), Korea, China, and Ukraine.
Generally speaking, kaolin from different countries, and even different deposits within the same country, differs in many respects due to variations in a number of kaolinite properties. Examples of such properties include degree of crystallinity, coarseness, brightness, levels of other compounds such as titania and iron oxide, particle size, particle shape, size and/or shape distribution. Variations in properties leads to differences in performance of the resultant kaolin products. For example, crystallinity impacts resultant brightness, whiteness, opacity, gloss, and viscosity of the resultant products. It is noted that opacity and gloss are application performance parameters while the other listed parameters are pigment attribute parameters. Particle size, shape, and distribution impacts the smoothness, optical properties, and flow properties of the resultant products. Smoothness and optical properties are application performance parameters while flow properties are pigment attribute parameters.
Kaolin based products are used in many applications including paints, paper coatings, agricultural compositions, fiberglass products, polymer and rubber compositions, ceramic applications, catalyst supports, pharmaceuticals, cosmetics, electrical components, adhesives, filter aids, and many more. Certain grades of kaolin having discrete properties are ideally suited for select applications. Accordingly, to maximize the quality of a resultant kaolin grade, kaolin crude is subjected to processing that yields a specifically desired grade of kaolin.
The paint industry supplies consumer-oriented products of the solvent and emulsion types. Solvent or so-called “oil based” paints are relatively simple systems, easy to formulate but difficult for the consumer to use. Solvent paint contains a binder (oil of resin), a solvent (thinner), drying agents and pigments. Alkyd paint is the most common kind of oil based paint, and many oil based paints are therefore normally referred to as alkyd paints. Alkyd is simply the name of the synthetic resin, usually containing a vegetable oil, that is used as the binder. Emulsion or so-called “latex” paints are complex mixtures containing latex surfactants, protective colloids, emulsifiers and water in addition to one or more types of pigment. Following their introduction after World War II, latex paints have substantially gained in market acceptance. Latex paints now account for a majority of interior and exterior paint trade sales.
Interior and exterior paints have generally similar formulations. An important distinction, however, is that exterior grade paints contain relatively more binder and prime pigment but less extender pigment than interior paints. This is because paint film integrity and overall durability are more critical in exterior paints than in interior grades. Accordingly, improved pigments and extender pigments are desired for exterior paints.